In general, an intake system of a motor engine is arranged to be fed with evaporated gas evaporated within a fuel tank. A feeding path therefor is called as a purge passage, and consists of the fuel tank; a canister taking in the evaporated gas evaporated in a fuel tank and temporarily adsorbing the gas therein; and a series of piping connecting the main elements such as the intake system of the engine etc, receiving the evaporated gas (purge gas) discharged from the canister. Further, an electromagnetic valve used for duty control of the flow rate of the purge gas is provided between the canister of the purge passage and the intake system of the engine.
Here, suppose that the intake system of the engine and the canister are connected by means of a single piping; a single electromagnetic valve is provided therebetween; and the electromagnetic valve is intermittently open and close controlled (duty control), to thereby control the flow rate of the purge gas flowing through the purge passage, the intermittent opening and closing of the electromagnetic valve produces pressure pulsations in the purge passage, and due to this, it makes nonuniform the feed rate of the purge gas relative to intake air and fuel mixtures into the engine, thus degrading the control of an air fuel ratio. Further, the purge passage leading from the fuel tank to the intake system of the engine through the canister and electromagnetic valve, and the electromagnetic valve are mounted on the vehicle. Therefore, vibrations originated from the pressure pulsations in the purge passage are propagated to inside the vehicle and generate noises therein.
Furthermore, in recent years, there has been a demand for the increased flow rate of the purge passage. The increased flow rate augments the pressure pulsations in the purge passage, and this has a tendency for the above-mentioned problems to be serious.
For that reason, it is conceivable to increase a control frequency for the duty control of the electromagnetic valve, as a method of reducing the pressure pulsations in the purge passage by using a single electromagnetic valve, e.g., to increase the control frequency from 10 Hz to 20 Hz.
However, although the method can reduce the pressure pulsations, the durability of the electromagnetic valve is decreased for the increased number of times of operation per unit time. Moreover, increasing the control frequency shifts a duty ratio that enables the electromagnetic valve to rise from a closed state to an opened state, to a high ratio, narrowing the control range and lowering the control resolution consequently.
With such circumstances as the background, various fuel-evaporated gas processing systems have been proposed so far, which have a structure where their purge passage is forked halfway at least into two directions as conventional fuel-evaporated gas processing systems. In all of those systems, an electromagnetic valve is provided in each of the pipes of the branched purge passages, and the electromagnetic valve is open and close driven by a duty control method in each of the branched purge passages. This reduces the purge gas supply of the flow rate to an intake system of an engine by means of the branched purge passages and at least two electromagnetic valves as compared with the flow rate in the case of using a single electromagnetic valve, thus suppressing the pressure pulsations in the purge passage including the branched purge passages (see Patent Document 1 to Patent Document 6, for example).
Patent Document 1: JP-B6-46017 (P. 3 and FIG. 2)
Patent Document 2: JP-A5-332205 ([0012] and FIG. 2)
Patent Document 3: JP-A6-272582 ([0018] and FIG. 2)
Patent Document 4: JP-A6-272628 ([0017] to [0024] and FIG. 1)
Patent Document 5: JP-A7-83129 ([0012] to [0015] and FIG. 1)
Patent Document 6: JP-A5-10767, a microfilm ([0006] to [0009] and FIG. 1)
At this, FIG. 12 is a chart showing the case where an electromagnetic valve A and an electromagnetic valve B are provided in the respective branched purge passages of a purge passage forked, and control timing of the electromagnetic valve B is controlled with a phase difference of ½ cycles (T/2) relative to that of the electromagnetic valve A.
According to the system, although control frequencies of the electromagnetic valve A and the electromagnetic valve B are as they were, e.g., 10 Hz, they are equivalent, taken the purge passage all together, to the case where the purge passage is controlled in a doubled control frequency, i.e., 20 Hz. Therefore, it can reduce the pressure pulsations in the purge passage without provoking lowering of the electromagnetic valve durability or raising of control resolution due to the increased control frequency.
However, the system shown in FIG. 12 shall produce pressure pulsations in 20 Hz, for example. In the meantime, since there are engines of various specifications, the system shown in FIG. 12 does not always match those engines. On this account, the appearance of a method of reducing the pressure pulsations by various techniques has been earnestly waiting for.
Moreover, in the system shown in FIG. 12, it lacks compactness of the components with the increase of their number as the electromagnetic valve A or the electromagnetic valve B are separately provided in the respective branched purge passages and individually control those electromagnetic valves.
Furthermore, in the technique shown in FIG. 12, while two electromagnetic valves are used and controlled with a phase difference of ½ cycles in order to double an apparent control frequency, a pressure response delay has not been considered at all from the time when an opening or a closing operation of the electromagnetic valve is executed to the time when the operation is reflected upon the response as a pressure fluctuation of the purge passage.
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a fuel-evaporated gas processing system or an electromagnetic valve device able to efficiently suppress the pressure pulsations in purge gas generated at the time of open and close driving of the electromagnetic valve, repress the degradation of control of an air fuel ratio resulting from the pressure pulsations, or effectually reduce the piping vibrations and pulse sound of the purge passage.